JP2007507507A - Aspartate derivative and method for producing the same - Google Patents

Abstract

The present invention relates to novel aspartates, their method of production and the use of these mono and polyaspartates as reactive components for polyisocyanates in two-component polyurethane coating compositions and for preparing polyurethane prepolymers.

Description

  The present invention relates to a novel aspartate, its production from primary amines and maleates, its use as a polyisocyanate-reactive component in a two-component polyurethane coating composition, and its use for the preparation of polyurethane prepolymers.

  Two-component coating compositions containing a polyisocyanate component combined with one or more isocyanate-reactive components as a binder are known. They are suitable for producing high quality coatings that are hard, elastic, abrasion resistant, solvent resistant and weather resistant.

  In the two-component surface coating industry, secondary polyamines containing ester groups have been used. Secondary polyamines are particularly suitable as binders in low solvent amounts or solvent free high solids coating compositions in combination with lacquer polyisocyanates because they can cure the coating rapidly at low temperatures.

  These secondary polyamines are polyaspartates, for example, U.S. Pat.Nos. 5,126,170, 5,214,086, 5,236,741, 5,243,012, 5,364,955, 5,412,056, 5,623,045. No. 5,736,604, No. 6,183,870, No. 6,355,829, No. 6,458,293 and No. 6,482,333, and European Patent Application No. 667,362. In addition, aspartates containing aldimine groups are also known (see US Pat. Nos. 5,489,704, 5,559,204 and 5,847,195). Their use as an isocyanate-reactive component alone or in combination with other isocyanate-reactive components in a two-component coating composition is also described in the above patents.

In the process for producing these polyaspartates, the corresponding primary polyamine is represented by the formula:
R ₃ OOC-C (R ₁ ) = C (R ₂ ) -COOR ₄
[Wherein R ₁ , R ₂ , R ₃ and R ₄ are the same or different organic groups. ]
Reacts with the corresponding maleate or fumarate to form secondary polyamines. Due to steric, structural and electronic effects, these secondary amino groups have a reactivity to isocyanate groups that is low enough to be mixed with polyisocyanates in a reliable and easy way.

  Prior art (Chem. Ber., 1946, 38, 83; Houben Weyl, Meth. D. Org. Chemie, 11/1, 272, 1957; and Usp. Chimii, 1969, 38) , 1933), the reaction used to prepare polyaspartate is the addition of a primary amine to an activated CC double bond in a vinylcarbonyl compound. However, it was found that this reaction was not completed during the course of the actual synthesis process (eg 24 hours with stirring at 60 ° C.). The actual degree of reaction depends on the type of primary polyamine. Thus, the conversion for 1,6-hexanediamine after 1 day (measured by the concentration of fumarate produced by the rearrangement of maleate in the presence of free unconverted maleate and base catalyst) is about 90-93%. The conversion after 1 day for alicyclic polyamines with sterically hindered primary amino groups, ie 4,4'-diamino-3,3'-dimethyldicyclohexylmethane, is only 77%. Complete or substantially complete conversion is achieved only after a few days or in the case of 4,4'-diamino-3,3'-dimethyldicyclohexylmethane only after a few months.

  A typical commercial production runs for 16 hours, at which point the conversion is complete at a value between 75 and 95%, depending on the amine used. “Unfinished” material is placed in a drum and stored until the reaction is complete. This storage is generally carried out for a period between 2 weeks and 6 months.

  US Pat. No. 5,821,326 describes the use of certain 5-membered aromatic compounds as catalysts to facilitate the preparation of aspartate.

［式中、
X は、（環状）脂肪族的に結合したアミノ基を含み、60〜6000 の数平均分子量を有し、イソシアネート基に対して反応性であるか又は 100 ℃までの温度でイソシアネート基に対して不活性である更なる官能基を含んでもよいモノ又はポリアミンから、1 級アミノ基を除去することによって得られた m 価の有機基を表し、
R₁ 及び R₂ は、同じか又は異なっていてもよく、水素、又は 100 ℃以下の温度でイソシアネート基に対して不活性である有機基を表し（好ましくは両方とも水素である）、
R₃ 及び R₄ は、同じか又は異なっていてもよく、100 ℃以下の温度でイソシアネート基に対して不活性である有機基を表し（好ましくは C₁〜C₈ であり、最も好ましくはメチル又はエチルである）、
R₅ は、C₂H₄、C₃H₆ 及び C₅H₁₀ からなる群から選ばれる基を表し、
a 及び b は 1〜5 の整数を表し、a と b の合計は 2〜6 であり、
R₅ が C₂H₄ 又は C₃H₆ を表すとき x は 1 であり、R₅ が C₅H₁₀ を表すとき x は 0 である。］
に相当するアスパルテートを対象とする。 The present invention has the formula:

[Where:
X contains a (cyclo) aliphatically bound amino group, has a number average molecular weight of 60 to 6000, is reactive to isocyanate groups, or is isocyanate groups at temperatures up to 100 ° C. Represents a m-valent organic group obtained by removing a primary amino group from a mono- or polyamine which may contain further functional groups which are inert,
R ₁ and R _{2, which} may be the same or different, represent hydrogen or an organic group that is inert to isocyanate groups at a temperature of 100 ° C. or less (preferably both are hydrogen);
R ₃ and R ₄ may be the same or different and represent organic groups that are inert to isocyanate groups at temperatures of 100 ° C. or less (preferably C _{1 to} C ₈ , most preferably methyl Or ethyl)
R ₅ represents a group selected from the group consisting of C ₂ H ₄ , C ₃ H ₆ and C ₅ H ₁₀ ;
a and b represent an integer of 1 to 5, the sum of a and b is 2 to 6,
When R ₅ represents C ₂ H ₄ or C ₃ H ₆ , x is 1, and when R ₅ represents C ₅ H ₁₀ , x is 0. ]
Aspartate equivalent to

The present invention
A) at a temperature of 0-100 ° C. in solution or in the absence of solvent,
a) Formula (II):
X [-NH ₂ ] _m (II)
Mono or polyamine corresponding to
b) Formula (III):
R ₃ OOC-C (R ₁ ) = C (R ₂ ) -COOR ₄ (III)
[Wherein, X, R ₁ , R ₂ , R ₃ and R ₄ are as defined above, and m represents an integer of 2 to 6]. ]
And a primary amino group in component a) from about 1.1: 1 to about 3.0: 1 in an equivalent ratio of the C = C double bond in component b), and
B) It also relates to a method for producing aspartate corresponding to the above formula, comprising the step of reacting the obtained product with a compound selected from the group consisting of ethylene carbonate, propylene carbonate and ε-caprolactone.

The present invention as a binder,
a) a polyisocyanate component,
b) b1) a compound corresponding to formula (I), and
b2) an isocyanate-reactive component optionally containing other isocyanate-reactive components, optionally including additives known in the surface coating art, with an equivalent ratio of isocyanate groups to isocyanate-reactive groups of about 0.8: 1 It also relates to a two-component coating composition, which is about 2.0: 1.

  Finally, the present invention provides a urea, urethane, allophanate and / or biuret structure based on the reaction product of a polyisocyanate and an aspartate of the present invention optionally mixed with one or more isocyanate-reactive components. It also relates to a prepolymer comprising

Polyamines useful in the present invention include i) high molecular weight amines having a molecular weight of 400 to about 10,000, preferably 800 to about 6,000, and ii) low molecular weight amines having a molecular weight of less than 400. The molecular weight is the number average molecular weight (M _n ) and is determined by end group analysis (NH 2 number). Examples of these polyamines are those in which an amino group is bonded to a carbon atom of an aliphatic compound, alicyclic compound, araliphatic compound and / or aromatic compound.

  Suitable low molecular weight polyamine starting compounds are ethylenediamine, 1,2- and 1,3-propanediamine, 2-methyl-1,2-propanediamine, 2,2-dimethyl-1,3-propanediamine, 1,3 -And 1,4-butanediamine, 1,3- and 1,5-pentanediamine, 2-methyl-1,5-pentanediamine, 1,6-hexanediamine, 2,5-dimethyl-2,5-hexane Diamine, 2,2,4- and / or 2,4,4-trimethyl-1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10- Decanediamine, 1,11-undecanediamine, 1,12-dodecanediamine, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 2,4- and / or 2,6-hexahydrotoluylene diene Amines, 2,4′- and / or 4,4′-diamino-dicyclohexylmethane, 3,3′-dialkyl-4,4′-diamino-dicyclohexylmethane (eg, 3,3′- Methyl-4,4'-diamino-dicyclohexylmethane and 3,3'-diethyl-4,4'-diamino-dicyclohexylmethane), 1,3- and / or 1,4-cyclohexanediamine, 1,3-bis ( Methylamino) -cyclohexane, 1,8-p-menthanediamine, hydrazine, semicarbazide carboxylic acid hydrazide, bis-hydrazide, bis-semicarbazide, phenylenediamine, 2,4- and 2,6-toluylenediamine, 2,3 -And 3,4-toluylenediamine, 2,4'- and / or 4,4'-diaminodiphenylmethane, polyfunctional polyphenylene polymethylene polyamine obtained by aniline / formaldehyde condensation reaction, N, N, N-tris- (2-aminoethyl) -amine, guanidine, melamine, N- (2-aminoethyl) -1,3-propanediamine, 3,3'-diamino-benzidine, polyoxypropyleneamine, polyoxyethyleneamine Min, 2,4-bis- (4′-aminobenzyl) -aniline and mixtures thereof.

  Preferred polyamines are 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane (isophoronediamine or IPDA), bis- (4-aminocyclohexyl) -methane, bis- (4-amino-3-methylcyclohexyl). ) -Methane, 1,6-diaminohexane, 2-methylpentamethylenediamine and ethylenediamine.

  Suitable high molecular weight polyamines are NCO prepolymers, except that the terminal hydroxyl group is converted to an amino group by amination or by reaction of the hydroxyl group with a diisocyanate followed by hydrolysis of the terminal isocyanate group to an amino group. Corresponds to the polyhydroxyl compound used to prepare the polymer. Preferred high molecular weight polyamines are amine-terminated polyethers, such as Jeffamine resin available from Huntsman.

A suitable optionally substituted maleate or fumarate suitable for use in the preparation of aspartate has the formula:
R ₃ OOC-C (R ₁ ) = C (R ₂ ) -COOR ₄
[Wherein R ₁ , R ₂ , R ₃ and R ₄ are as defined above. ]
It is equivalent to. Examples are dimethyl ester, diethyl ester, di-n-butyl ester and mixed alkyl esters of maleic acid and fumaric acid, and the corresponding maleic ester or fumaric acid substituted in the 2nd and / or 3rd position by methyl. Contains esters. Maleates or fumarate suitable for preparing the aspartate of the present invention are dimethyl maleate, diethyl maleate, di-n-propyl maleate, di-isopropyl maleate, di-n-butyl maleate and di-2. -Ethylhexyl maleate, methyl ethyl maleate or the corresponding fumarate.

  The aspartate of the present invention is produced by first reacting component a) and component b) at a temperature of 0-100 ° C, preferably 20-80 ° C, more preferably 20-60 ° C. Here, the equivalent ratio of the primary amino group in component a) to the C = C double bond equivalent in component b) is about 1.1: 1 to about 3.0: 1, preferably about 1.1: 1 to about 2.0: 1 The reaction time can be between about 1 and about 4 hours, depending on the type of polyamine and the desired maximum residual concentration of reactants in the reaction mixture. The resulting product is then reacted with a compound selected from the group consisting of ethylene carbonate, propylene carbonate and ε-caprolactone. This second reaction is generally carried out at a temperature of about 50 to about 100 ° C. for a time in the range of about 1 to about 4 hours. The ratio of reactants is selected so that one mole of ethylene carbonate, propylene carbonate or ε-caprolactone is present for each unreacted amine group.

  The method for producing aspartate of the present invention may be performed either in a solution or in the absence of a solvent. After the synthesis step, for example, a solvent may be added to reduce the viscosity. Suitable solvents include any organic solvent, preferably those known in the surface coating art. Examples include acetone, methyl ethyl ketone, methyl isobutyl ketone, n-butyl acetate, methoxy-propyl acetate, toluene, xylene and higher aromatic solvents (eg, Solvesso solvent from Exxon).

  The aspartate produced according to the present invention can be used directly as a polyisocyanate-reactive component after completion of the synthesis process.

One use of the aspartate of the present invention is as a binder,
a) a polyisocyanate component, and
b) b1) aspartate of the present invention,
b2) To produce a coating from a two-component coating composition that optionally includes an isocyanate-reactive component containing other known isocyanate-reactive components.

  Suitable polyisocyanate components a) are known and include polyisocyanates known in polyurethane chemistry, such as low molecular weight polyisocyanates and lacquer polyisocyanates prepared from these low molecular weight polyisocyanates. Lacquer polyisocyanates known from the surface coating technology are preferred. These lacquer polyisocyanates contain biuret groups, isocyanurate groups, allophanate groups, uretdione groups, carbodiimide groups and / or urethane groups, and are preferably prepared from (cyclo) aliphatic polyisocyanates.

Low molecular weight polyisocyanates suitable for use in the present invention or for preparing lacquer polyisocyanates are polyisocyanates having a molecular weight of from 140 to 300, such as 1,4-tetramethylene diisocyanate, 1,6- Hexamethylene diisocyanate (HDI), 2,2,4- and / or 2,4,4-trimethyl-hexamethylene diisocyanate, dodecamethylene diisocyanate, 2-methyl-1,5-diisocyanatopentane, 1,4-di Isocyanatocyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanato-methylcyclohexane (IPDI), 2,4- and / or 4,4'-diisocyanato-dicyclohexyl-methane, 1-isocyanato-1- methyl-3 (4) - isocyanatomethyl - cyclohexane (IMCI), 2,4 and / or 2,6-hexahydrotoluylene diisocyanate (H ₆ TDI), 2,4及And / or 4,4′-diisocyanatodiphenylmethane or mixtures of these isomers and higher homologues (obtainable by known methods by phosgenation of aniline / formaldehyde condensates), 2,4- and / or 2,6-diisocyanatotoluene, and mixtures thereof. The use of low molecular weight polyisocyanate itself is not preferred. Also less preferred are aromatic polyisocyanates such as lacquer polyisocyanates prepared from 2,4- and / or 2,6-diisocyanatotoluene. Urethane group-containing lacquer polyisocyanates are preferably based on low molecular weight polyhydroxyl compounds having a molecular weight of 62 to 300, such as ethylene glycol, propylene glycol and / or trimethylolpropane.

  Preferred lacquer polyisocyanates for use as component a) are based on 1,6-hexamethylene diisocyanate and have an NCO content of 16 to 24% by weight and a maximum viscosity of 10,000 mPa · s, preferably 3000 mPa · s at 23 ° C. It is what has.

Component b1) is selected from the aspartate of the present invention. Preferably X is 1-amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane (IPDA), 4,4'-diaminocyclohexylmethane (HMDI), 3,3'-dimethyl-4,4 '-Diaminodicyclohexylmethane (Lasomin C260 from BASF), hexahydro-2,4- and / or 2,6-diaminotoluene (H ₆ TDA), C-monomethyl-diaminodicyclohexyl-methane isomer, 3 (4)- A divalent hydrocarbon group obtained by removing an amino group from aminomethyl-1-methylcyclohexylamine (AMCA), hexanediamine or 2-methyl-5-pentanediamine.

Particularly preferred starting components b1) include aspartates where R ₃ and R ₄ represent C ₁ -C ₈ alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, 2-ethylhexyl.

  Optional starting component b2) is a known compound containing at least two isocyanate-reactive groups, including groups that react with isocyanate groups under the action of moisture or / and heat. Examples include hydroxy functionalized polyacrylates and polyester polyols. Mixtures of these compounds can also be used.

  In the binder used in the present invention, the amount of components a), b1) and (optionally) b2) is such that the equivalent ratio of isocyanate groups to isocyanate-reactive groups is from about 0.8: 1 to about 2.0: 1, preferably It is chosen to be about 0.8: 1 to about 1.2: 1.

  The binder of the present invention is prepared by mixing the components in the absence of a solvent or in the presence of a solvent commonly used in polyurethane surface coating technology. Suitable solvents include ethyl acetate, butyl acetate, methoxypropyl acetate, methyl isobutyl ketone, methyl ethyl ketone, xylene, N-methylpyrrolidone, petroleum spirit, chlorobenzene, Solvesso solvent or mixtures thereof.

  Preferably, the weight ratio of binder components a) and b) to solvent in the coating composition of the present invention is from about 40:60 to about 100: 0, more preferably from about 60:40 to about 90:10.

  The coating composition may also contain additives known in the surface coating art. Additives include pigments, fillers, flow control agents, catalysts and anti-settling agents.

  The properties of the coating obtained from the coating composition according to the invention can be adjusted by appropriate selection of the types and proportions of the starting components a), b1) and b2).

  The coating composition can be applied to any substrate in a single layer or multiple layers by known methods, such as spray coating, paint coating, dip coating, flow coating, or methods using a roller or spreader. The coating composition according to the invention is suitable for producing a coating on a substrate such as metal, plastic, wood or glass. The coating composition is particularly suitable for coating steel sheets used in the production of car bodies, machinery, cladding panels, containers and containers. Prior to applying the coating composition of the present invention, the substrate may be treated with a suitable primer. The coating can be dried at a temperature of about 0-160 ° C.

  The method for producing a coating composition using aspartate of the present invention can also be used for producing a prepolymer containing urea, urethane, allophanate and / or biuret structure.

  In contrast to conventional aspartate, almost complete conversion is achieved, so that the aspartate of the present invention can be used directly after completion of the synthesis process. As a result of the low concentration of maleate, fumarate and / or primary amino groups, these products are not only toxicologically and physiologically harmless, but also moderate in contrast to violent reactivity to isocyanates. Shows reactivity. Because of their low viscosity, they become suitable substitutes for organic solvents that pollute the environment used conventionally as reactive diluents, and thus high solids that are high quality, low solvent or even solvent-free. Can be used in two-component coating compositions.

  All parts and percentages are by weight unless otherwise indicated.

Example 1
A round bottom flask was equipped with a stirrer, heating mantle, nitrogen inlet, thermocouple and addition funnel. 210 g (2 eq) bis- (paraaminocyclohexyl) methane (PACM) was introduced into the flask at room temperature. 172 g (1 equivalent) of diethyl maleate was added via addition funnel over 30 minutes. The temperature of the flask rose to 35 ° C. The reaction was heated to 60 ° C. and maintained for 7 hours. At this point the degree of unsaturation was 0.69 mg maleic acid / g resin indicating that the reaction was 99% complete. The reaction mixture was cooled to room temperature. 102 g (1 equivalent) of propylene carbonate was added over 30 minutes. The temperature was raised to 60 ° C and maintained for 1.5 hours. At this time, the amine value was 116 (theoretical amine value was 116.2). The product had a viscosity of 52,000 mPa · s at 25 ° C.

Example 2
The above procedure was repeated except that 116 g (2 equivalents) of hexanediamine (HDA) was used. The amine value was 149 (theoretical amine value was 143.6). The product had a viscosity of 850 mPa · s at 25 ° C.

Examples 3 and 4
The coating composition was prepared by mixing with Desmodur N-3300 at 100% solids. (Desmodur N-3300 is a hexadiisocyanate-based trimer from commercially available Bayer Polymers LLC having an NCO content of about 22%, a viscosity of about 2500 mPa · s at 25 ° C, and an NCO equivalent of about 193. The resin was mixed with N3300 with NCO / (OH-NH) = 1.05. The material was stirred twice to ensure proper mixing. The materials and amounts used are shown in the table below.

  The end point of the pot life was measured as the point at which the material was hardened enough to allow the container to lift easily upon stirring. The drying time was controlled using a 6-hour meter for curing and drying in a constant temperature and humidity chamber. The hardness was measured the day after curing using the Shore D test.

Example 5
A round bottom flask was equipped with a stirrer, heating mantle, nitrogen inlet, thermocouple and addition funnel. 58 g (1.00 eq) of Dytek A was introduced into the flask at room temperature. 86.0 g (0.5 eq) diethyl maleate was added in one portion. The temperature of the flask rose to 35 ° C. The reaction was heated to 60 ° C. and maintained for 5 and a half hours. At this point the degree of unsaturation was 0.35 mg maleic acid / g resin indicating that the reaction was 99% complete. 57.2 g (0.5 eq) of ε-caprolactone was added in one portion and heated at 60 degrees for 5 days. The final degree of unsaturation was 0, indicating that the reaction was 100% complete. The amine value was 143 (theoretical amine value was 139). The product had a viscosity of 300 mPa · s at 25 ° C.

Example 6
A round bottom flask was equipped with a stirrer, heating mantle, nitrogen inlet, thermocouple and addition funnel. 57.2 g (0.5 eq) of ε-caprolactone was introduced into the flask at room temperature. 58 g (1.00 eq) Dytek A was added in one portion. The reaction was heated at 60 ° C. for 6 hours, at which point the amine number was 256 (theoretical amine number was 253) mg KOH / g resin. 86.0 g (0.5 eq) diethyl maleate was added in one portion and heated at 60 degrees for 6 and a half hours. At this point the degree of unsaturation was 1.12 mg maleic acid / g resin indicating that the reaction was 96% complete. The next day, the unsaturation was 0.58, indicating that the reaction was 98% complete. The amine number is 143 (theoretical amine number is 139) and the product has a viscosity of 1820 mPa · s at 25 ° C.

  Although the invention has been described in detail above for purposes of illustration, such details are for purposes of illustration only and are intended to be from the spirit and scope of the invention, except as limited by the claims. It will be understood that changes can be made by those skilled in the art without departing.

Claims (4)

formula:

[Where:
X contains (cyclo) aliphatically bonded amino groups, has a number average molecular weight of 60 to 6000, is reactive towards isocyanate groups, or is isocyanate groups at temperatures up to 100 ° C. Represents a m-valent organic group obtained by removing a primary amino group from a mono- or polyamine which may contain further functional groups which are inert,
R ₁ and R _{2, which} may be the same or different, represent hydrogen or an organic group that is inert to isocyanate groups at a temperature of 100 ° C. or less,
R ₃ and R ₄ may be the same or different and represent an organic group that is inert to isocyanate groups at a temperature of 100 ° C. or less,
R ₅ represents a group selected from the group consisting of C ₂ H ₄ , C ₃ H ₆ and C ₅ H ₁₀ ;
a and b represent an integer of 1 to 5, the sum of a and b is 2 to 6,
When R ₅ represents C ₂ H ₄ or C ₃ H ₆ , x is 1, and when R ₅ represents C ₅ H ₁₀ , x is 0. ]
Aspartate equivalent to. formula:

[Where:
X contains a (cyclo) aliphatically bound amino group, has a number average molecular weight of 60 to 6000, is reactive to isocyanate groups, or is isocyanate groups at temperatures up to 100 ° C. Represents a m-valent organic group obtained by removing a primary amino group from a mono- or polyamine which may contain further functional groups which are inert,
R ₁ and R _{2, which} may be the same or different, represent hydrogen or an organic group that is inert to isocyanate groups at a temperature of 100 ° C. or less (preferably both are hydrogen);
R ₃ and R ₄ may be the same or different and represent organic groups that are inert to isocyanate groups at temperatures of 100 ° C. or less (preferably C _{1 to} C ₈ , most preferably methyl Or ethyl)
R ₅ represents a group selected from the group consisting of C ₂ H ₄ , C ₃ H ₆ and C ₅ H ₁₀ ;
a and b represent an integer of 1 to 5, the sum of a and b is 2 to 6,
When R ₅ represents C ₂ H ₄ or C ₃ H ₆ , x is 1, and when R ₅ represents C ₅ H ₁₀ , x is 0. ]
A method for producing aspartate equivalent to
A) at a temperature of 0-100 ° C. in solution or in the absence of solvent,
a) Formula (II):
X [-NH ₂ ] _m (II)
Mono or polyamine corresponding to
b) Formula (III):
R ₃ OOC-C (R ₁ ) = C (R ₂ ) -COOR ₄ (III)
[Wherein, X, R ₁ , R ₂ , R ₃ and R ₄ are as defined above, and m represents an integer of 2 to 6]. ]
And a primary amino group in component a) from about 1.1: 1 to about 3.0: 1 in an equivalent ratio of the C = C double bond in component b), and
B) A method comprising a step of reacting the obtained product with a compound selected from the group consisting of ethylene carbonate, propylene carbonate and ε-caprolactone. As a binder
a) a polyisocyanate component, and
b) b1) aspartate according to claim 1,
b2) A two-component coating composition comprising an isocyanate-reactive component optionally containing other isocyanate-reactive components, wherein the equivalent ratio of isocyanate groups to isocyanate-reactive groups is from about 0.8: 1 to about 2.0: 1.   A prepolymer containing urea, urethane, allophanate and / or biuret structure, containing the reaction product of polyisocyanate and aspartate according to claim 1.